The present invention relates to a rolling contact bearing which is suitable for use in a special environment where lubricants, such as grease or oil, cannot be used, particularly in a high temperature clean environment and in a clean environment.
For example, in the field of semiconductor production, the line width of electric circuit is becoming smaller as the degree of integration of semiconductors increases, forming a trend toward a laminar structure (2-story). Thus, in the sputtering process and so on, wafers have come to be treated at higher temperature (up to about 500.degree. C.). For this reason, bearings disposed in wafer transfer systems or the like are expected to be heated to about 400.degree. C., causing fears of the lubricating property of the lubricant being lowered owing to its high temperature deterioration, the bearing life being thereby decreased, and the bearing inner clearance becoming too large or too small owing to thermal expansion of the bearing components, which phenomena adversely affect such properties of the bearing as durability and low dust producing property.
Further, the recent advance in the degree of device integration has resulted in a high level standardization of the degree of cleanness of clean rooms, requiring that bearings used in such clean environment have a particularly desirable low dust producing property.
At present, there is no bearing available which can be used and exhibits good durability in said high temperature clean environment or in an environment where the ambient temperature is not so high but where a high degree of cleanness is required.
In this connection it is to be noted that in said high temperature special environment, the reason for the fear that the lubricating property of the bearing would be lowered is as follows: Whereas as lubricants for bearings which are run in a highly clean vacuum environment, such as one found in semiconductor production facilities, use is often made of solid lubricants of high polymers, such as PTFE, with which the bearings are coated. However, since these high polymers have relatively low heat resistance temperatures (for example, about 320.degree. C. even for PTFE, which is superior in heat resistance), in an environment where the bearing temperature is expected to exceed the heat resistance temperature of solid lubricants, there is a possibility that they fail to perform their functions as lubricants. On the other hand, soft metals, such as gold, silver and lead or laminar materials, such as molybdenum disulfide, produce a relatively large amount of dust and are inferior in durability in the atmosphere. Therefore, in a device, such as a wafer transfer device, which frequently traverses between atmosphere and vacuum, there is a fear of the bearing life being shortened.
As for bearings which are used in a high temperature clean environment, it is insufficient to simply secure heat resistance for the bearing components themselves; it is necessary to take measures by paying due considerations to lubricating property, low dust producing property, and operability in both atmosphere and vacuum. If the ambient temperature is not so high, lubricating property, low dust producing property and operability in both atmosphere and vacuum become important characteristics.